The surface of a thin-film recording disk is divided into a textured landing zone adjacent the inner-diameter, where the read-write head in a hard drive can land on the disk, and a data zone extending from the landing zone to the outer diameter of the disk.
The purpose of the texturing in the landing zone is to reduce start-stop stiction when the head lands on the disk at a start or stop condition. Without texturing, high stiction would exert occasionally catastrophic forces on the read-write head. The texturing in the landing zone must have a certain minimum roughness factor in order to avoid this type of high-stiction problem.
Typically, a thin-film media disk is textured by texturing the disk substrate, e.g., a nickel-phosphorus-coated aluminum substrate or glass or ceramic substrate, then sputtering various thin film layers on the substrate surface to form the thin-film media. Since the thin-film layers adopt the texture patterns of the underlaying substrate, the final disk has about the same texture features, i.e., roughness features, as the originally textured substrate.
With a greater emphasis on higher data density and lower flying heights in a hard disk, there is increased need for landing-zone texturing that provides adequate roughness, but with low-height surface texture features. In particular, with fly heights currently approaching less than 1.mu. in, it is important that the landing zone texture features themselves have sub-1.mu. in heights.
The need for carefully controlled surface texture roughness and feature height has encouraged the development of laser-zone texturing (LZT). By directing laser pulses of desired energy at surface areas on a spinning substrate, bumps with desired height and diameter distributions can be formed. By selecting suitable pulse frequencies and substrate rotational rates, known bump densities are achieved.
Because of the critical need to achieve laser bumps within a given height distribution, it is important to monitor laser bump characteristics, either during laser-zone texturing, to provide feedback control for laser-ablation power settings, or to examine textured substrates prior to sputtering, as part of a quality control program to ensure that finished media will have the desired bump height distribution characteristics.